The American Petroleum Institute (API) has set industry standards for the nondestructive inspection of oil field tubular goods. The standard as to whether a flaw in the wall of a pipe is acceptable or unacceptable is based on the depth of the flaw as a percentage of the wall thickness of the pipe. For threaded couplings that join pipes together, the standard for acceptability or unacceptability is based on the absolute depth of the flaw, irrespective of the wall thickness of the coupling. Oil field casing and tubing supplied by a pipe manufacturer commonly is threaded at both ends and one of the ends has an internally threaded coupling member secured to, or made up on, one end of the casing or tubing. Similarly, used casing and tubing available in the field commonly has a coupling threaded onto one end of the tubular member. API inspection standards require that any flaw that extends from the body of the tubular member under the end of the threaded coupling be considered a reject, regardless of the depth or nature of the flaw. This requirement stems from the fact that such a flaw may extend into the threaded region of the member, which is considered to be a critical area in terms of joint strength and makeup integrity. Any flaw at the end of the coupling that extends axially at the end of the coupling also is considered unacceptable.
In the past, automatic or semi-automatic nondestructive inspection of tubular members having a coupling threaded thereon has been somewhat incomplete because the apparatus could not inspect the region of the pipe immediately adjacent the inward end of the threaded coupling, and could not inspect the adjacent end region of the coupling. Consequently, the inspection results produced by automatic inspection equipment cannot be certified as meeting API standards, and the region immediately adjacent the end of the threaded coupling had to be inspected by an operator using a hand held inspection device. This manual inspection is quite time consuming, cumbersome, and can be dangerous to the operator when performed in a semi-automated inspection operation that involves a high volume of tubular members.
The present invention is a novel mechanism for permitting an eddy current probe of an automatic inspection apparatus to move very closely into the region between a pipe wall and the end of the coupling threaded thereon, and then to automatically hop over the end of the collar and come down at the very end of the top surface of the coupling. The invention thus enables an automatic end-area inspection apparatus to detect flaws at the inward end area of the coupling and in the pipe wall immediately adjacent thereto. This enables the detection of flaws that require an absolute rejection of that joint. Similarly, by being able to move in very close to the end of the coupling, the apparatus is able to determine that an acceptable flaw terminates just short of the end of the coupling and that the pipe is acceptable, rather than having to reject the pipe as it would if the inspection apparatus could not determine with certainty whether or not the flaw extended under the coupling.